1. Field of the Invention
The present invention is directed to a device for filtering a ray bundle of electromagnetic radiation, particularly an X-ray bundle, of the type having different filter stages with multiple filters that can be adjusted into the ray bundle, a drive for moving the filters and having a separate arm for each filter, a first end of each arm engaging at appertaining filter and the other end thereof being chargeable with a force generated by the drive.
The invention is also directed to an assembly having a depth-of-field diaphragm arrangement for a medical X-ray system.
2. Description of the Prior Art
In a medical X-ray apparatus, the “quality” of the radiation, i.e. the energy distribution of the X-ray quanta, is significantly defined by filtering in addition to the voltage at the X-ray tube. Above all, low-energy quanta that do not significantly contribute to the imaging, and lead only to an unnecessary exposure of the patient to radiation, are to be eliminated by filtering the X-rays. The center of gravity of the energy distribution is shifted toward higher values by the filtering—the radiation is “hardened”. Aluminum and—given higher-energy radiation—copper are frequently employed filter materials.
Copper pre-filters with different filter stages, i.e. with different absorption values, are particularly required for cardiological examinations.
A filter changer with different filter stages is disclosed by German OS 198 32 973. In order to be able to introduce more than two different filters (for example, filter A, filter B, filter C) into the beam path, a separate electromagnet must thereby be present for each filter, which leads to a complicated design that is susceptible to malfunction. An advantage of the filter changer of German OS 198 32 973 having respective, separate drives is that the filters can be introduced in combinations into the beam path (for example, filter A+filter C).
German PS 42 29 319 discloses another filter changer having a number of filters that can be introduced into the ray bundle and that are different from one another. Only a single motor is required for introducing the filters. The filters can be successively introduced into the ray bundle against the force of spring elements by rotation of a shaft driven by the motor. The return movement ensues due to the force of the spring elements. Separate switches are required and are present for holding the filters in the beam path against the spring force, the switches switching the motor off after the appropriate filter is positioned in the beam path. In this filter changer, only one of the existing filters can be positioned in the beam path an any one time (for example, filter B after the resetting of filter A, filter C after the resetting of filter B). The number of filter stages thus is limited to the number of existing filters since combinations of the filters in the beam path (for example, filter A+filter C) are not possible.